The research is designed to assess the relationship between the reinforcing properties of psychoactive drugs and personality, mood states and subjective reactions to the drugs in humans. These relationships will be assesed in a situation where subjects are given an opportunity to choose to ingest one of two available drugs with concurrent measurements of subjective effects. In one group of studies these relationships will be investigated in specific populations of subjects (anxious, depressed, overweight and heavy drinkers) using stimulants and anxiolytics. If reinforcing effects are greater in certain populations of subjects this may indicate that they are at a greater risk for dependence. In other studies, a similar preference procedure will be used with subjects remaining in the laboratory in order to test a broad spectrum of drugs including anxiolytics, stimulants, barbiturates, alcohol and opiates. The purpose of these studies is to further refine our methods for determining the dependence potential of drugs and as well, to use these methods to determine whether there are certain individuals who possess psychological characteristics which put them at greater risk for excessive drug use.